A 29-year-old actor who plays Dustin Hoffman's grandson in a new film, Barney's Version. In real life, he's actually Hoffman's son. The film is adapted from the much-loved Canadian Mordecai Richler's last novel.

Who's the missing link? Who plays Hoffman Jr's dad?

Paul Giamatti. He plays Barney and, as he says, it's like the genes jumped a generation: "Jake looks nothing like me. Or Rosamund." That would be Rosamund Pike, who plays his mother.

Aren't they too young? They must have conceived him in primary school.

Heavens no, it's not that kind of film. It spans four decades, narrated by Barney, a second-rate producer of slap-and-tickle TV. By the time we get to his kids, we're on prosthetics.

So how is Hoffman Sr?

He plays an ex-cop ageing disgracefully. He's great.

And how much of Jake's rise can we put down to his old man?

Definitely some of his early bit parts. His first on-screen appearance was "boy at the pancake counter" in Rain Man.

What next?

Anyone looking to cast a Graduate remake? Honestly, he's a dead ringer. In the meantime, he stars in an indie vampire flick: Rosencrantz and Guildenstern Are Undead.